The long term objective of the proposed research is to analyze the immune function of accessory cells in the lung and to relate these to immune responses triggered as a result of foreign antigens. Dendritic cells (DC), one of the most potent accessory cells, have recently been identified and isolated from the lung and upper airways. In this proposal, experiments are designed to characterize phenotypically and functionally the DC of upper airways and lungs of Lewis rats ad to examine factors that may be involved in their regulation. The specific aims are to determine by ultrastructural, immunocytochemistry the ontogeny of DC in the lung and upper airways of fetal/newborn rats and to examine in vitro the ability of these newly differentiated cells to induce antigen (hen egg lysozyme, HEL) and lectin mediated (Con A) T- cell proliferation. The capacity of cytokines (IL-1, IL-6, GM-CSF, IFN- gamma) to accelerate the maturation of these early DC will be tested. The migration pattern of DC to the lung and local lymph nodes will be examined in a bio-distribution study using intravenously injected 111 In-labeled, low density bone marrow DC precursors. Following the intravenous injection of 3 H-uridine labeled DC, the distribution in tissue will be determined by autoradiography on immunocytochemically reacted sections of the lung and upper airways. Using purified DC isolated from adult rat lungs, monoclonal antibodies (MAb) will be developed that react specifically with rat DC for the identification and isolation of these cells. The MAb will be screened further to identify MAb that recognize, on the surface of DC, putative adhesion molecule(s) that mediate T-cell binding, as well as mitogenic molecule(s) that stimulate T-cells proliferation. Studies will inhibitors and cytokines on isolated lung DC, will examine the requirements for DC to T-cell clustering. The capacity of cytokines (IL-1, IL-4, IL-6, GM-CSF, TNF alpha and IFN-gamma) to regulate the accessory cell function of lung DC, as measured by allogeneic MLR and antigen and lectin mediated T-cell responses, will be tested in vitro and in vivo. The possibility that lymphokine activated killer (LAK) T-cells may down-regulate DC activity will be examined in vitro on lung DC isolated from IL-2 treated rats. Conversely, treatment in vitro of lung DC with either IL-2 or in vitro generated LAK cells will be used to determine whether IL-2 or LAK cells directly affect accessory cell function of DC in culture. Results from these studies should lead to a better understanding of the role of DC in the immune defense of the lung and the factors that regulate their activities.